I'm a developer that would like to put my app out for betatesting. Does anyone know what I need to do on my end to make this work? I see people asking for a live id.. and then what?

Just proceed in the App Hub to normally submit an application. In the first screen, you can choose to list the app as beta. This means that it won't need to be certified, it won't appear in public Marketplace listings, and that you also need to pre-approve Windows Live IDs for downloading the beta app. You can update these IDs at any time, even after submission. From my experience, it takes 24 hours before a beta app becomes available for download (you do receive a download link within a couple of hours though). Updating beta tester IDs seems to go live almost instantly.